South Australia has shut its border to Western Australia after a hotel quarantine worker in Perth tested positive for COVID-19.
The border closure, which applies to all of WA, came into effect late on Sunday night following an announcement from SA Police.
The SA government says anyone who has entered the state from WA since January 26 must self-quarantine and get a COVID-19 test.
People can apply for permission to travel from WA to SA for essential purposes.
That includes South Australian returning home from WA. They must apply to cross the border.
The approach taken by SA is more severe than other states, which also brought in travel restrictions.
Victoria, Northern Territory, Tasmania and Queensland closed its border to areas affected by a five-day WA lockdown.
The closures are in response to a security guard at the Sheraton Four Points hotel in Perth testing positive for coronavirus.
Authorities believe the man has probably contracted the highly contagious UK variant of the virus.
It comes only a day after SA lifted restrictions for travellers from the wider Sydney region.
South Australia reported no new COVID-19 cases on Sunday and has no active infections.